The Japanese journal of animal reproduction
Print ISSN : 0453-0551
Effects of gonadotrophins on maturation and ovulation of oocytes in adult rats.
II. Cytological observation on the time of ovulation.
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1977 Volume 22 Issue 4 Pages 130-138


Preovulatory changes and the time of ovulation were studied in adult rats treated with various doses (0 to 50 i. u.) of gonadotrophins. A total of 235 rats were raised under artificial lighting condition (darkness from 1 a. m. to 11 a. m.). They were injected with pregnant mare serum gonadotrophin (PMS) at 3 p. m. in early diestrus and human chorionic gonadotrophin (HCG) at 9 p. m. in proestrus (at 54 hours' interval, or 4 hours before the beginning of darkness). These rats were killed 12, 16, and 20 hours after HCG injection (or 8, 12, and 16 hours after the beginning of darkness). At autopsy, ovulated ova were counted. Then the ovaries of each rat were fixed in Bouin's solution and stained with Heidenhain iron hematoxylin. In them, oocytes in follicles of 300μ or over in diameter were examined for the stage of maturation division.
The results obtained are as follows.
1. In untreated rats ovulation was almost completed 8 hours after the beginning of darkness.It was delayed, however, in superovulation-treated rats even when an appropriate dose of HCG (more than 1/2 or 1/3 of the dose of PMS) had been injected. The time of complete ovulation in relation to the HCG injection (time in hours after the beginning of darkness is shown in parenthesis) was estimated as follows: a dose of 10 i. u. of PMS, 16 (12) hours; a dose of 20 i. u. of PMS, 16 (12) hours or later up to 20 (16) hours; a dose of 30 to 50 i. u. of PMS, about 20 (16) hours.
2. The percentage of a total of mature and ovulated oocytes to a total of oocytes in follicles of 300 μ or over in diameter was 48.2, 35.6, 28.1, and 19.2% in rats injected with 50, 30, 20, and 10 i. u. of PMS, respectively, together with the same dose of HCG. It was 15.8% in the untreated control rats. In those treated rats, the percentage was reduced with decrease in the dose of HCG. It was reduced slightly, however, when rats had been treated with such a dose of HCG as cor-responding to more than 1/2 of the dose of PMS. (It was 92.5 to 97.8, as expressed by index to 100 which represented the percentage in the case of injection with th same doses of PMS and HCG.)
3. The correlation (γ) between a sum total of mature plus ovulated oocytes and a total of oocytes contained in follicles of 300 μ or over in diameter was calculated to be 0.787, 0.555, and 0.288 in rats treated with 50, 30, and 20 i. u. of PMS, respectively, together with more than 1/2 of the respective dose of HCG.
From these results, it seems that the number of ovulated ova may depend on the number of oocytes contained in large follicles of the ovaries in superovulation-treated rats. At present, however, it is difficult to draw any conclusion. Further studies are needed to verify this presumption.

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